Recently, as the imaging element is advanced in function, the function of the video camera is diversified. For example, a CMOS type imaging element is used in a video camera, and high-speed reading or partial reading of video signals may be easier, and a slow-motion function capable of recording at higher speed and reproducing is realized. However, to realize the slow-motion function, it is required to handle signals at data rate several times higher than in the standard system. To realize the slow-motion function, therefore, a special structure other than the imaging element and its driving method are needed.
To solve the problems, for example, patent document 1 discloses a method. FIG. 14 shows a configuration of an imaging device disclosed in patent document 1. The imaging device shown in FIG. 14 has a high-speed imaging function for imaging at higher speed (for example, three times higher) than in ordinary mode, in addition to the imaging operation at ordinary speed.
An imaging section 1401 includes an imaging element, its drive circuit, and an analog signal processing circuit. The imaging section 1401 converts an optical image signal into an electrical signal and outputs the electrical signal as an output. An A/D converter 1402 converts an analog video signal, that is, the output signal from the imaging section 1401, into a digital video signal, and feeds it into a camera signal processing circuit 1403. The camera signal processing circuit 1403 processes the signals as required in an ordinary camera, such as gain adjustment, gamma correction or contour correction, and the output signals become video signal of standard form to be recorded and displayed.
In the case of three-times-high-speed imaging, as compared with ordinary speed, for example, video signal of 60 fields per second, it is necessary to generate video signals of 180 fields per second. In the imaging section 1401, when a signal charge is imaged out at three times of ordinary speed from the imaging element, video signals are output in every 1/180 second, that is, ⅓ time of ordinary mode. To handle this imaging signal, the A/D converter 1402 and the camera signal processing circuit 1403 must operate at three times of ordinary speed.
The output from the camera signal processing circuit 1403, that is, the video signal of three times of ordinary speed is compressed in a compression circuit 1405. The compressed video data is recorded in a recording medium 1406. The recording operation of the recording medium 1406 is controlled by a control circuit 1408, and is recorded at three times of ordinary speed. That is, the video data of one field portion is recorded in every 1/180 second.
The video imaged at high speed is reproduced by “slow reproduction” operation as explained below. In reproduction, the control circuit 1408 controls the recording medium 1406, and reads out the data from the recording medium 1406 at a rate of 60 fields per second, same as in ordinary video signal. The output data is decoded in an decompression circuit 1407 by reverse processing of data compression, and is returned to a form of video signal. As a result, the video signal is output in every 1/60 second, same as in the ordinary mode, and the video signal expanded three times in the time axis as compared with the imaging time is obtained.
In high-speed imaging of three times of ordinary speed, the video signal of three times of speed output from the camera signal processing circuit 1403 is recorded in the recording medium 1406 as mentioned above, and is simultaneously supplied into a speed converting circuit 1404, and is converted into a video signal of ordinary speed. This video signal is displayed as a monitor image during imaging process. The speed converting circuit 1404 extracts video signals at a rate of three fields to one field, from the video signal of 180 fields per second, and produces a video signal of 60 fields per second.
A selector 1409 selects the video signal to be sent to an output terminal 1410, and specifically selects an a-side signal at the time of high-speed imaging, and a b-side signal at the time of slow reproduction. That is, at the time of high-speed imaging, the video signal of three times of speed is recorded in the recoding medium 1406, and the video signal converted to ordinary speed is simultaneously output, so that the image being imaged can be displayed on the monitor. When reproducing the video imaged at high speed, the video signal recorded in the recording medium 1406 is reproduced at ⅓ speed of recording speed, so that a slow reproduction signal can be obtained.
Patent document 1: JP-A-2005-295423.